1. Field of Invention
The present invention relates to the provision of ordered repeating microgeometric patterns to bone and tissue interface zones of dental implants, to effect enhanced adhesion to soft tissue and osseointegration of an implant to bone.
2. Prior Art
Numerous publications establish that cell attachment growth, migration and orientation, as well as extracellular matrix synthesis and orientation thereof, are moderated by substrate surface shape (i.e., microgeometry) as well as by surface chemistry. However, the findings in such publications do not address what effect different substrate microgeometrics and dimension would have on various cell colonies"" growth and migration parameters as opposed to the morphology of individual cells. Thus, while the prior art establishes that surface microgeometry of substrates influences cell orientation, it does not disclose or suggest what effect different surface microgeometry as implants would have on either the rate or direction of the cell colony growth of different cells of soft tissue or bone surrounding or abutting such a substrate.
Surface microgeometry interaction between soft tissue or bone and implant surfaces has been demonstrated on ceramic and metallic orthopedic implants. This interaction indicates that smooth implant surfaces promote the formation of thick fibrosis tissue encapsulation and that rough implant surfaces promote the formation of thinner, soft tissue encapsulation and more intimate bone integration. Smooth and porous titanium and titanium alloy implant surfaces have been shown to have different effects on the orientation of fibrous tissue or bone cells in vitro. In addition, surface roughness was demonstrated to be a factor in tissue or bone integration into implants having hydroxyapatite surfaces and to alter the dynamics of cell attachment and growth on polymer implants whose surfaces had been roughened by hydrolytic etching.
From the examination of in vitro growth characteristics of cells cultured on flat surfaces there have evolved the following cell xe2x80x9cbehavioralxe2x80x9d characteristics:
1. attachment-dependent growth: the dependence of normal diploid cell or substrate attachment for normal growth;
2. density-dependent inhibition: the tendency of such cells to slow or stop growing once a confluent monolayer is formed;
3. substrate-exploring function: the ability of some types of cells to migrate on a surface in search of acceptable areas for attachment and growth; and
4. contact guidance: the ability of some types of cells to migrate and orient along physical structures. J. L. Ricci, et al Trans.Soc.Biomat. 17.253 (1991); J. L. Ricci, et al, Tissue-Inducing Biomaterials, Mat. Res. Soc. Symp. Proc. 252,221-229 (1992); J.Ricci, et al., Bull.Hosp. Joint. Dis. Orthop. Inst. supra; J. L. Ricci, et al, J. Biomed Mater Res. 25(5), supra.; D. M. Brunette, et al, J. Dent. Res., 11-26 (1986); P. Clark, et al. Development, 108, 635-644 (1990).
The behavioral characteristic of cellular contact guidance has been demonstrated in vitro on a variety of surfaces such as grooved titanium, grooved epoxy polymer, and collagen matrix materials of different textures and orientations. Grooved machined metal and polymer surfaces have also been shown to cause cellular and extracellular matrix orientation in vivo and to encourage or impede epithelial downgrowth in experimental dental implants. B. Cheroudi, et al. J Biomat. Mater. Res. 24. 1067-1085 (1990) and 22. 459-473 (1988); G. A. Dunn, et al supra; J. Overton, supra; S. L. Shor. supra; R. Sarber, et al, supra.
Substrates containing grooves of different configurations and sizes have been shown to have orientating effects on fibroblasts and substrates containing grooves of varying depth have been shown to have different degrees of effect on individual cell orientation establishing that grooved surfaces can modulate cell orientation in vitro and can cause oriented cell and tissue growth in vivo. For example, it has been shown that fibrous tissue forms strong interdigitations with relatively large grooves in the range of about 140 xcexcm and can result in an effective barrier against soft tissue downgrowth perpendicular to the grooves. It has also been shown that smaller grooves on the order of about 3-22 xcexcm were more effective in the contact guidance of individual cells. D. M. Brunette, et al. Development, supra; P. Clark et al, supra.
The findings in these publications do not address what effects different substrate microgeometries and sizes would have on various cell colonies growth and migration parameters as opposed to morphology of individual cells. That is, these publications do not disclose or suggest what effect different surface microgeometry of implants would have on either the rate or direction of the cell colony growth of different cells and different tissues surrounding an implant. In addition, these publications do not disclose or consider the most effective textured substrate or crude microgeometry for controlling cell colony growth.
The current methods used to texture the surfaces of dental implant elements typically employ sand, glass bead and alumina grit blasting techniques, and acid etching techniques, of the implant surface. In sand, glass bead or alumina grit blasting techniques, compressed air is generally used to drive a blasting medium onto the implant surface at a high velocity to deform and, in some instances, remove portions of the implant surface. The surface texture obtained depends upon the size, shape and hardness of the implant material and on the velocity at which the blasting medium is driven onto the implant surface. The most common surfaces produced by sand or glass bead blasting are matte or satin-finish, while alumina grit blasting produces a random roughened surface.
In acid etching techniques a pattern or mask is placed upon that surface of the implant desired not to be texturized. The exposed parts are then typically treated with an acid that corrodes the exposed surface of the implant whereupon the acid treated surface is washed or neutralized with an appropriate solvent and the pattern or mask is removed.
Illustrative of the sand or glass bead blasting technique is the method disclosed in U.S. Pat. No. 5,057,208 to H. R. Sherry, et al wherein the implant surface is shot blasted with metal shot followed by glass bead blasting and then electropolishing.
Illustrative of an acid etching technique is the method disclosed in U.S. Pat. No. 4,778,469 to R. Y. Lin, et al wherein an acid soluble (e.g., aluminum or zinc) space occupier is used. The space occupier contains the pattern to be transferred to the implant surface and is placed on the desired portion of the implant surface that is to be texturized. The space occupier is pressed into the implant surface and is then removed by treating it with acid.
It has been found that these typical blasting techniques leave debris from the processing materials embedded in the implant surface as contaminants. This debris has also been found in soft tissue isolated from the areas adjacent to failed press-fit total hip replacements indicating that the debris was released from the surface of the implants. These problems of residual contaminants debris have been overcome by using the use of laser systems which produces texturized microgeometric substrates without introducing embedded, particulate contaminants. See, for example, U.S. Pat. Nos. 5,645,740 and 5,607,607 to Naiman and Lamson. This instant invention refines and extends the teaching thereof with particular reference to dental implants. The prior art is also characterized by implants intended for use in soft tissue, such as U.S. Pat. No. 5,011,494 to Von Recum, et al and its related patent family. Therein, texturized surfaces of implants are provided with a variety of geometric configurations which comprise a plurality of projection and recesses formed in a three-dimensional body. It is therein specified that the mean bridging, breadth and diametric distances and dimension play a role in optimizing cell anchorage to implant surfaces. However, the teaching of Von Recum is not applicable to hard bone-like organic tissue, as exists in a dental implant environment.
Another reference which employs randomized roughing of an implant is U.S. Pat. No. 5,571,017 (1996) to Niznick which, although addressing the area of dental implants, does not employ an ordered or pre-established repetitive microgeometric surface pattern. Similarly, U.S. Pat. No. 4,320,891 (1982) to Branemark employs a randomly micro-pitted surface to create pores in a range of 10 to 1000 nanometers (one micrometer). See FIG. 36. Further, Branemark states that the optimal results in his system are obtained with pore diameters equal to or smaller than about 300 nanometers. Therein, although Branemark indicates that his implant surfaces may assume a pattern of grooves, corrugations or channels, such geometries are not ordered or repetitive, and it is apparent that the range of focus thereof is in the range of 0.3 to 1 micron in terms of diameters or width of such structures, whereas the lowest end of these invention relate to alternating ridges and grooves having a minimum width of six microns and extending in width to about 15 microns, the same based upon clinical studies as are more fully set forth below. Further, based upon the much smaller surface dimensions with which Brenemark is concerned, it is clear that the focus of Brenemark is that of individual cell growth, this as opposed to promotion of rate, orientation and direction of entire colonies of cells, i.e., the object of the present invention.
U.S. Pat. No. 4,752,294 (1988) to Lundgren refers to tissue ingrowth channels and openings having a dimension of about 30 microns. Accordingly, the dimension of interest to Lundgren is well in excess of the maximum dimension (25 microns) of concern in the present invention. Further, the teaching of Lundgrin is fundamentally that of a guide or element, of substantially three-dimensional character, for facilitating directed tissue regeneration. The present invention relates only to surface textures and does not address tissue regeneration.
U.S. Pat. No. 4,553,272 (1985) to Mears relates, as in Van Recum above, to the development of porous implants having pore sizes in a range of 25 to 400 microns, that is, a minimum range which is well in excess of the maximum range applicable to the ordered microgeometric repetitive surface patterns taught herein. Also, in view of the large dimension of the channels taught by Mears, no relationship exists or is suggested between cell size, structure size, and cellular control resultant thereof.
U.S. Pat. No. 5,004,475 (1991) to Vermeire relates to a hip prosthesis having channels or grooves which, similarly, to Mears, are intended to promote tissue ingrowth but which do not correlate between surface microgeometry, cell size, and cell growth. Further Vermeire does not teach any preferred structure or dimension for the channels or grooves thereof.
Patents such as U.S. Pat. No. 5,094,618 (1992) to Sullivan and 5,316,478 (1994) to Chalifoux teach the use of threaded dental post for endodontic use in association with dental restorations and improved securement between the restoration and a surviving tooth portion. Such references employ substantially random projections of a dimension much greater than that contemplated by the present invention, however, primarily differ from the in instant invention from the lack of teaching of ordered, repetitive, surface patterns within the applicable range in order to obtain advantageous characteristic of growth of colonies of cell at the interface between a maxillofacial bone and/or tissue and a dental implant and/or abutment element.
Thereby, all prior art of record addresses the issue of bone adhesion to an implant at either a level of tissue ingrowth entailing a dimension well above that set forth herein or relates to control of the growth or orientation of individual cells, as opposed to cell colonies, which resultingly require employment of surface characteristics of dimensions substantially smaller than that employed by the within inventors.
The invention relates to a dental implant system comprising implant element for surgical insertion into a maxillofacial bone or tissue of a patient, the implant element having a collar section and a distal, anchor-like section, said collar section having an ordered microgeometric repetitive surface pattern in the form or a multiplicity of alternating ridges and grooves, each having a fixed or established width in a range of about 2.0 to about 25 microns (micrometers) and a fixed or established depth in a range of about 2 to about 25 microns, in which said microgemoetric repetitive patterns define a guide for preferential promotion of the rate, orientation and direction of growth colonies of cells of said maxillofacial bone or tissue which are in contact with said surface pattern.
It is accordingly an object of the invention to provide microgeometic surfaces which alter the growth behavior of colonies of cells attached thereto.
It is another object to provide microgeometric surfaces of the above type having cross-sectional configurations, which are preferential to particular cell or tissue types.
It is a further object to provide microgeometric implant substrate for controlling in vivo cell attachment, orientation growth, migration and tissue function and therein having dimensions preferential for the prevention of cell growth in a first-axis and for the inducement of growth along a second axis.
It is a further object to provide repetitive microgeometric texturized configurations to implants applicable in a variety of medical applications.
The above and yet other objects and advantages will become apparent from the hereinafter-set forth Brief Description of the Drawings, Detailed Description of the Invention and Claims appended herewith.